A package is a container that holds your application components such as Custom Objects, Apex code, Apex triggers, Visualforce pages, and so on. This makes up your application. While there are other ways to move components between Salesforce orgs, a package provides a container that you can use for your entire application or deliver optional features by leveraging the so-called extension packages.
There are two types of packages, managed and unmanaged. Unmanaged packages result in the transfer of components from one org to another; however, the result is as if those components had been originally created in the destination org, meaning that they can be readily modified or even deleted by the administrator of that org. They are also not upgradable and are not particularly ideal from a support perspective. Moreover, the Apex code that you write is also visible for all to see, so your Intellectual Property is at risk.
Unmanaged packages can be used for sharing template components that are intended to be changed by the subscriber. If you are not using GitHub and the GitHub Salesforce Deployment Tool (https://github.com/afawcett/githubsfdeploy), they can also provide a means to share open source libraries to developers.
This book focuses solely on managed packages. Managed packages have the following features that are ideal for distributing your application. The org where your application package is installed is referred to as a subscriber org, since users of this org are subscribing to the services your application provides:
The naming scope: Your component names are unique to your package throughout the utilization of a namespace. This means that even if you have object X in your application, and the subscriber has an object of the same name, they remain distinct. You will define a namespace later in this chapter.
The governor scope: Code in your application executes within its own governor limit scope (such as DML and SOQL governors that are subject to passing Salesforce Security Review) and is not affected by other applications or code within the subscriber org. Note that some governors such as the CPU time governor are shared by the whole execution context (discussed in a later chapter) regardless of the namespace.
Upgrades and versioning: Once the subscribers have started using your application, creating data, making configurations, and so on, you will want to provide upgrades and patches with new versions of your application.
There are other benefits to managed packages, but these are only accessible after becoming a Salesforce Partner and completing the security review process; these benefits are described later in this chapter. Salesforce provides ISVForce Guide (otherwise known as the Packaging Guide) in which these topics are discussed in depth; bookmark it now! The following is the URL for ISVForce Guide: